Automatic telephone system



. Aug. 12,- 1930. J. wlcKs AUTOMATIC TELEPHONE SYSTEM 10 Sheets-Sheet 1.

Original Filed Aug. 26, 1926 & Mg S \Q g g mm w John Mmks J. WICKS1,772,472

10 Sheets-Sheet 2 -ImrEn m" I John Mmks Aug, 12, 1930.

AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 26, 1926 Aug; 12, 1930.

' J. WICKS AUTOMATIC TELEPHONE SYSTEM 10 Sheeis-Sheet 3 Original FiledAug. 26,1926

John Mmks Aug. 12, 1930. 7 J. WICKS AUTOMATIC TELEPHONE SYSTEM OriginalFiled Aug. 26. 1926 10 Sheets-Sheet 4 J. WICKS AUTQMATIC TELEPHONESYSTEM Original Filed Aug. 26, 1926 John Inluzks M 1 mg.

J. WICKS AUTOMATIC TELEPHONE SYSTEM Aug. 12, 1930.

Original Filed Aug. 26, 1926 10 Sheets-Sheet 6 FITITT:

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AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 26, 1926 10 Sheets-Sheet8 Qisk Juhn Inlmks Aug. 12, 1930. J. WICKS 7 AUTOMATIC TELEPHONE SYSTEHOriginal Filed-Aug. 26, 1926 10 Sheets-She et 9 m m W Nam Aug. 12, 1930.J w c s AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 26, 1926 v 10Sheets-Sheet 1O atented An. 12, 1930 JOHN WICKS, DE UAR PARK, ILLINOIS,ASSIGNOR '10 AUTOMALKIC ELECTRIC INC., 01? GHICAGO, ILLINOIS, ACORPOTION OF DELAWARE AUTOMATIC TELEPHONE SYSTEM Application filed.August 26, 1926-Serial No. 131,575. Renewed hecember 1e, 19%.

This invention relates to telephone systems in general, but is moreparticularly concerned with automatic telephone systems in whichconnections are. established through 5 the medium of subscribercontrolled automatic switches. In such a system, automatic switches suchas a first selector, one or more intermediate selectors, and a connectorare successively operated under the control of a dial at the callingstation. This invention further pertains especially to that kind ofautomatic telephone system in which the motor magnets of the automaticswitches aredirectly operated by current impulses produced by the linerelay'of the first selector, the line relay of the first selector beingoperated by impulses produced by the dial of the calling statifin.

An automatic telephone system of this kind, known as a direct pulsingsystem, is disclosed in the inventors copending application Serial No.8,343, filed Febfll, 1925. In the system disclosed in the aboveapplication, the current impulses for operating the motor magnets of theautomatic switches are produced by the line relay of the first selector(better termed, the first selector repeater) and are transmitted to themagnets of the first selector repeater and to the magnets of so thesucceeding switches over one of the talking conductors of the extendedtrunk line. While this method of control is entirely satisfactory forswitch operation in a single exchange, loop control (control over thetwo conductors of the trunk line in series) is recognized as being mostpreferable for controlling switch operations, especially whenconnections between exchanges are extended. In the former case thedifference in ground potential between any two exchanges,

which may vary between wide limits from time to time, constantlythreatens proper switch operation when such operation is controlledovera single conductor. In the pres- 5 ent invention, the possibility ofthis condition causing trouble is entirely eliminated, for

the reason that the control of the magnets of the switches is affectedover the two trunk conductors in series.

The main object of this invention, therefore, is the provision of newand improved automatic switches for use in a direct puls ing automatictelephone system. The main feature resides in the circuit arrangementwhereby the current impulses for operating the magnets of the switcheproduced by the line relay of the first selector repeater, aretransmitted to the magnets of the switches over the two sides of theextended -trunk line in series.

Other objects are accomplished and various features are contained in theinvention which will be fully described in the body of thisspecification with the aid of the accompanying drawings.

Referring now to the accompanying drawings comprising Figs. 1-12, Figs.1-1O show by means of the usual schematic circuit diagrams a sufficientamount. of the apparatus in a multi-ofiice telephone system embodyingthe principles of this invention to enable the invention to be clearlydescribed and understood.

Fig. 11 is a diagram showing how the drawings upon which Figs. 1-8appear are to be arranged, (Fig. 8 to be substituted for Fig. 3 asdirected hereinafter) to be most intelligently understood in connectionwith the descriptions of the establishment of certain connections to begiven. Fig. 12 likewise is a diagram showing how the drawings upon whichFigs. 2, 8-10 appear may be arranged (Fig. 10 to be substituted forFigs. 2 and 7 as directed hereinafter) to be best understood inconnection with the descriptions of the establishment of certain otherconnections to be given also. The following paragraphs give a briefdescription of each of the above figures.

Fig. 1 shows the subscriber substation A whose line terminates at theexchange in the individual lineswitch LS, and is accessible to a groupof connectors by way of conductors 101'103'. The lineswitch LS, withother similar lineswitches has access to a group of first selectorrepeaters of which the selector repeater SR is one. In the banks of theselector repeaters access is had to the outgoing trunks to the otheroifices in the system, a group of trunks to each ofiice being accessiblein a separate level; in one certain level access is had to a roup ofreverting call switches, and in anot or level access is had to a groupof local second selectors. The dial tone machine DT, for producing adial tone current supply, the supervisory equipment, comprisin relays181 and 182 and lamps LL an the subscribers meter M, are also shown inFig. 1. The substation A is of the usual automatic type- The lineswitchLS is of the well known rotary type having no normal position and movingin one directlon only, being advanced upon the back stroke of theassociated step ing magnet. The selector repeater SR mec anica-lly is ofthe usual Strowger vertical and rotary type. The circuits of selectorrepeater SR form a particular part of this invention and will bedescribed in detail in later paragraphs.

Fig. 2 shows the local second selector S and the local third selector8*. The selector S is one of the group of local second selectorsaccessible in a certain level in the banks of the first selectorrepeaters. In the banks of this group of second selectors, access is hadto the various groups of local third selectors, the selector S being oneof a certain roup. In the banks of third selectors access is ad to thevarious groups of connectors. It is also assumed that the exchange inquestion has a sub-office. Trunks to the sub-office are accessible in acertain level in the local second selector terminating thereat inincoming third selectors, similar to incoming selector IS, Fig. 4. p

The selectors S and S are identical in mechanical and circuit detailsand are of the well known Strowger vertical and rotary type. Thecircuits of these intermediate selectors are modified to meet therequirements of the invention and will be described in detailhereinafter.

Fig. 3 shows the connector C which is one of a certain group ofregularconnectors accessible in the banks of the group of third selectorscontaining selector S (and also in the banks of the group of tolltransmission selectors containing toll transmission selector TTS, Fig.6). In the banks of the connector C access is had to a group of linesextending to substations, the line to substation- A" being one of these.This line also terminates in the individual lineswitch LS Below theconnector C the ringing equipment, comprising the generator G andinterrupter T, the ground interrupter I, and the busy machine BM areshown.

Mechanically the connectorC is of the well known Strowger vertical androtary type. The circuits of the connector also form a part of theinvention and will be described in detail in following paragraphs. Thesubstation A" and the lineswitch LS are in all respects like thesubstation A and lineswitch. LS, shown in Fig. 1, except that inlineswitch the system. The incoming trunks from the other ofiiceslikewise terminate in similar incoming second selectors. The banks ofthe incoming second selectors are directly multipled with the banks ofthe local second selectors, and the incoming second selectors arethereby given'common access to the various groups of local thirdselectors.

The incoming selector IS mechanically is also of the Strowgerverticaland rotary type. The circuit arrangement, forming a particular part ofthis invention, will be described in detail hereinafter.

The right-hand half of Fig. 5 shows the incoming toll selector TS. This,toll selector terminates one of the toll trunks 'incomin from theofiice in which the main toll boar is located. As many incoming tolltrunks, terminating in similar incoming toll selectors, are provided asare necessary to carry the traflic to the ofiice in question. In thebanks of the'incoming toll selectors, access is had to groups of tolltransmission selectors, and also to a grou of trunks extending to thesub-oflice of the 0 co in question these trunks also terminating at thesub-office in similar toll transmission selectors.

The toll selector switch TS is of the ordinary Strowger vertical androtary type and is operated according to. the well known two wire systemof control. Special off-normal springs are provided however, to adapt itfor use in the system being described.

The left-hand half of Fig. 5 shows the toll operators cord CO by meansof which toll connections are established over trunks ex-' tending tothe various ofiices in the system, each trunk terminating at the tollboard in a jack such as jack J. This cord is of standard type and formsno particular part of the invention itself. The circuit thereof will bedescribed only in so far as is necessary to fully describe otherapparatus controlled by means within the cord.

Fig. 6 shows the toll transmission selector TTS, which is one of acertain group of toll transmission selectors accessible in the banks ofthe incoming toll selectors. The banks of the toll transmissionselectors are directly multipled with the banks of the local thirdselectors, and the toll transmission selectors and local third selectorsare thereby given common access to the connectors.

Mechanically, the toll transmission selector TTS is also of the Strowgervertical and rotary type. The circuit arrangements, however, have beenmodified to meet the requirements of the invention and will likewise bedescribed in detail hereinafter.

Fig. 7 shows the frequency selecting connector FSC which is in allrespects like connector C, Fig. 3, mechanically and in the method ofoperation, except that it is provided with an individual frequencyselecting mechanism FS which is operated responsive to "a digit toselect-the frequency of ringing current to be applied to the calledline. In

its banks access is had to party lines. The

frequency selecting connector FSC is one of a group offrequency-selecting connector-s accessible in the banks of a certaingroup of local third selectors multipled with the banks of a certaingroup of toll transmission selectors, which in this case will also beassumed to be the same group having access to the group of regularconnectors containing connector C. One party line, accessible toconnector FSC, serving substations A'-A-', and terminating at theexchange in the lineswitch LS is shown. The substation A shown in full,and also the other substations, only the bells of which are shown, arein all respects like the substation A, Fig. 1, except that the ringersare normally connected from one or the other side of the line to earthinstead of being normally bridged across the line conductors. LineswitchLS is in all respects like lineswitch LS Fig. 3. A description of theoperation of connector FS'C will be given in so far as it differs fromthe operation of connector C.

Fig. 8 shows the rotary connector RC, which is also like the connectorC, Fig. 3, except that it performs an automatic rotary hunting movementafter completing its rotary directive movement. In its banks, access ishad to groups of lines extending to private branch exchanges with thenumber of the first line assigned as the call number of the entiregroup. The rotary connector RC is one of a group of rotary connectorsaccessible in the banks of a certain group of local third selectorsmultipled with the banks of a certain group of toll transmissionselectors, which in this case will be assumed to be the same grouphaving access to the group of connectors containing connector C. Thefirst and last trunk-of a group extending to the private branch exchangeX, accessible to connector RC, are shown. minates in an individuallineswitch such as LS at the main exchange, and in a ack such as jack J8 at the branch exchange. The lineswitch LS is in all respect likelineswitch LS shown in Fig. 3. A description of the operation ofconnector BC in so far as it differs from the operation of connector C,Fig. 3, will also be given.

Fig. 9 shows the first selector repeater SR which is very similar to thefirst selector repeater SR, Fig. 1, the difierence in the two casesresiding in the mannerin which the operation of the subscribers meter iscontrolled. The first selector repeater SR is adapted to control theoperation of the subscribers me- Each trunk terter over a fourthconduct-or, while the first selector repeater SR is adapted to controlfourth wi er is omitted in lineswitch LS", and

the meter 9 is connected to the private normal conductor 902' and ismarginally adjusted.

Fig. 10 shows the reverting call switch RV, which, with other similarreverting call switches, is accessible in a certain level-in the banksof the first selector repeaters. The reverting call switch RV is also ofthe Showger vertical and rotary type, its circuits being modified,however, to meet the requirements of the invention, as will be describedin detail in later paragraphs.

In the lower right-hand corner of Fig. 10 the special ringing equipmentis shown, comprising the five ringing generators (which may be the samegenerators indicated in Fig. 7), the interrupting relay 7 4 andinterrupter T. The interrupter T comprises two commutators withconducting and insulating segments as shown, and wipers for eachrotating on the same shaft.

With this general description of the ob jects of the invention, thefeatures, and the apparatus used, in mind, a further understanding andappreciation of the invention may be gained from a detailed descriptionof the operations performed in the establishment of various connectionsbetween subscribers. For this purpose it will first be assumed that thesuscriber at substation A wishes to establish a connection with thesubscriber at substation A", (drawings to be arranged as shown in Fig.11).

Gall from. substation A to substation A" To initiate a call, thesubscriber at substation A first removes his'receiver. Removing thereceiver at the substation A places a bridge across the line conductors101 and 103,

thereby closing a circuit for the line relay 1 trunk upon which theswitch wipers are posifrom ground onthe test contact engaged by battery.

" idle trunk line.

- switching relay 105 is prevented from operthe test wiper 118, armature110 and the resting contact, armature 114 and the working contact,interrupting contacts 115 through the-winding of the stepping magnet 108to Accordingly stepping magnet 108 operates in a buzzer like manner toadvance the switch wipers 117120 in search of an During this operationating by reason of the ground potential on both ends of its winding.

7 When an idle trunk line is reached, stepping magnet 108 ceases tooperate, and relay 105, being no longer short circuited, energizes inseries with the stepping magnet 108.

tepping magnet 108 does not operate over this circuit due to therelatively high resistance of the Winding of relay 105. In operating,relay 105 prepares a circuit for the subscribers meter M at armature111, prepares'a holding circuit for itself at armature 110 and theworking contact, and at armatures 109 and 112 disconnects the lineconductors from the line relay 106 and ground, and extends the talkingconnection by way of these armatures and their working contacts, wipers117 and 120, conductors 121 and 124, normally closed contacts controlledby armatures 137 and 141, normally closed contacts controlled byarmatures 155 and 156, through the lower and upper windings of the linerelay 126 tov battery and ground, respectively. Line relay 126 operatesand closes a circuit for the release relay 127 at armature 142 and theworking contact. Release relay 127 operates and performs the followingcircuit changes: At armature 144 ground potential is placed on therelease conductor 122, thereby marking the trunk to first selectorrepeater SR busy and also completing a holding circuit for line relay106 of the lineswitch LS, this taking place before the slow acting linerelay 106 has had time to release its armatures. At armature 147 acircuit for the lower winding of holding relay 128 is prepared. Atarmatures 145 and 146' an initial energizing circuit for holding relay128 is closed, which may be traced from ground by way of armature 150and the resting contact, working contact and armature 145, normallyclosed springs controlled by armature 162, armature 160 and the restingcontact, armature 146 and the working contact, resistance 136, throughthe upper winding of relay 128, armature 158 and the resting contact,resting contact-and armature 141, normally closed springs controlled byarmature 164, through the upper winding of series relay 129, through thewinding of vertical magnet 133 to battery;

Relay 128 operates over this circuit and by the actuation of armatures148 and 152 establishes a new ener 'zing circuit for itself. Th1scircuit exten s from round at normally closed contacts control ed byarmature 129, through the winding of vertical magnet 133 to batteryoi Atarmature 150 a circuit is closed for the lamp L in series with relay181. Lamp L lights and relay 181 operates. The purpose of the lamp L andrelay 181 will be described later. By the operation of arma-' ture 150,direct ground is removed from release conductor 122', ground now beingsupplled thereto through the upper winding of relay 125,

The first selector repeater SR is now in condition to receive the'firstseries of impulses to be dialed by the calling subscriber, all the aboveoperations having taken place responsive to the removal of thereceiverat the calling substation. Furthermore, as soon as the wipers of thelineswitch LS are rotate'd into engagement with the trunk extending tothe then idle first selector repeater SR, a dial tone is transmitted tothe calling subscriber from the dial tone machine DT to which conductor193 is connected. Hearing this tone indicates to the calling subscriberthat he may commence dialing the number of the desired subscriber. I

In response to the dialing of the first. digit of the called number, theloop across the line conductors 101 and 103 is opened a correspondingnumber of times, thereby opening the circuit and causing a correspondingnumber of deenergizations and reenergizations of the line relay 126.Each time that relay 126 releases its armature 143, the resistance 136and the upper winding of relay 128 are short circuited. The resistanceof the upper winding of relay 128 is relatively high compared to theresistance of the upper Winding of re lay 129 and the resistance of thewinding of vertical magnet 133. The short circuiting of resistance 136and the upper winding of relay 128 therefore permits an increase in thecurrent flow through the vertical magnet 133 suificient to cause theoperation of the magnet each time the said resistance and winding isshort circuited. Thus vertical magnet 133 operates to step the switchwipers opposite winding of relay 127 to battery and also to.

battery over a parallel circuit including arma ture 142 and the restingcontact and resistance 136'.

Series relay 129 is also energized in series with vertical magnet 133,and by reason of its slow acting characteristic is maintained operatedduring the operation of vertical magnet 133. In operating, relay 129closes an initial energizing circuit for stepping relay 131 whichextends from ground on release conductor 122, working contact-andarmature 153, armature 163 and the resting contact, ofi-normal-springs166 which are closed upon the first vertical step of the switch wipers,through the winding of the stepping relay 131 to battery; Relay 131operates and closes a holding circuit for'itself at armature 160 whichmay be traced from ground through the upperwinding of relay 125, workingcontact and armature 145, normally closedsprings controlled b armature162, armature 160 and the wor ing contact, interrupting springs 165,off-normal .sprin s 166, through the winding of relay 131 to a ttery.The circuit of the stepping magnet 134 is also prepared at armature 159.

At the termination of the impulses of the. first digit, relay 129deenergizes and opens the initial energizing circuit of relay 131 atarmature 153. This armature, in releasing, allows the springs controlledthereby to close and complete the circuit for stepping magnet 134.Magnet 134 o crates and rotates the switch-wipers 1711 3 into engagementwith the first set of bank contacts in the selected level and also opensthe holding circuit for stepping relay 131 at interrupting springs 165.Relay 131 deenergizes and in turn opens the circuit of stepping magnet134 at armature 159, also opening its own locking circuit at armature160. Magnet 134 deenergizes and again closes interrupting springs 165.It the trunk terminating in this set of bank contacts is busy at thistime, ground potential will be present on the test contact upon whichthe wiper 172 is positioned. A circuit will again be closed for steppingrelay 131 from round on this test contact, wiper 172, armature 162 andthe resting contact, interrupting springs 165, off-normal springs 166through the winding of relay 131 to battery. Relay 131 will againoperate to close the circuit of stepping magnet 134, which thereuponenergizes and rotates the switch wipers into en-' gagement with the nextset of bank contacts as previously described. This stepping operation isrepeated until an idle trunk is found, which is indicated by the absenceof ground potential on the associated test contact.

It will be assumed that the first idle trunk in the selected level atthis time is the trunk comprising conductors 174-176. When the switchwipers 171-172 are rotated into engagement with the set of bank contacts17 4-176' terminating this trunk, no circuit is closed for the steppingrelay 131. Consequently the switch wipers are arrested in. thisposition. Furthermore, since no ground potential is applied to the upperterminal of theswitching relay 132, the following circuit becomeseffective to cause the energization of the switching relay 132; groundthrough the upper Winding of relay 125, working contact and armature145, through the winding of relay 132, interrupting contacts 165, 011-normal springs 166, through the winding of relay 131 to battery. Thecurrent flow in this circuit, limited by the comparatively highresistance of relay 132, is insuflicient to cause the energization ofrelay 131. Relay 132 operates, however, and performs the followingcircuit changes: Ground potential is supplied to the release conductor175 of the selected trunk by way of upper winding of relay 125, workingcontact and armature 145, working contact and armature 162, and wiper172, and the test contact 17 5 to which the conductor'175 is connected.A point in the circuit for operating the subscribers meter M is closedat armature 163, At armatures 161 and 164 the control circuit isextended by way 3 of Wipers 171 and 173, bank contacts 174 and 17 6,conductors 17 4 and 176 to the local second selector S The normal groundand battery connections to the upper and lower talking conductors aredisconnected at the springs controlled by armatures 161 and 164. Thecontrol circuit now extends from ground at normally closed springscontrolled by arms. ture 208 of second selector S conductor 174, bankcontact 174', wiper 171, armature-161 and the working contact, armature137 and the resting contact, armature 148 and the working contact,armature 146 and the working contact, resistance 131, upper winding ofrelay 128, working contact and armature 152, resting contact andarmature 141, working contact and armature 164, wiper 173, bank contact176, conductor 17 6, normally closed springs controlled by armature 211,winding of relay 202, through the winding of vertical magnet 204 tobattery. The application of ground potential to release conductor 17 5closes a circuit extending by way of the normally closed contactscontrolled by armature 209 through the upper winding of the two-steprelay 201 to battery. The energizetion of the upper winding of relay201.causcs the operation of armature 21.0 only. This operation merelyopens a point in the circuit of release magnet 206 and prepares othercircuits to be described later.

In response to the next digit dialed by the subscriber at substation A,resistance 136 and the upper winding of relay 128 are again shortcircuited a corresponding number of times. I This causes the operationof the vertical magnet 204 in a manner similar to the way in whichvertical magnet 133 of the first selector repeater SR was operated. Inoperating, ma net 204 steps the wipers 221-223 opposite the level ofbank contacts corresponding to the digit dialed. Relay 202, whichoperates in series with the vertical magnet 204 and due to itsslow-acting characteristics remains operated during the transmission ofthis series of im ulses, closes a circuit which may be traced fromground by way of armature 210 and the working con,- tact, workingcontact and armature 212, offnormal springs 218 which are closed uponthe first vertical step of the switch wipers, through the winding ofstepping relay 203 to battery. Stepping relay 203 operates and closes aholding circuit for itself at arma ture 213-and prepares a circuit forstepping magnet 205 at armature 214. At the termination of this seriesof impulses series relay 202 deenergizes and, by permitting-the closureof the springs controlled by armature 212, closes a circuit for steppingmagnet 205. Magnet 205 operates and rotates the switch wipers 221223into engagement with the first set of bank contacts in the selectedlevel, and also opens the holding circuit of stepping .relay 203 atinterrupting springs 215. Stepping relay 203 deenergizes and opens acircuit of the stepping magnet 205. In releasing, stepping magnet 205again closes interrupting contacts 215. If the trunk terminating in thisset of bank contacts is busy, ground potential will be present on thetest contact engaged by test wi er 222, and a circuit will again beclosed or relay 203 from ground on said test contact, wiper 222,armature 209 and the resting contact, interrupting contacts 216,interrupting contacts 215, off-normal springs'218, through the windingof relay 203 to battery. The alternate operation of the stepping relay203 and magnet 205 now takes place in a manner identical to the way inwhich stepping relay 131 and stepping magnet 134 of the first selectorrepeater SR operated,- thereby causing the selector S to position itswipers on the first set of bank contacts terminating an idle trunk line,an idle trunk line again being indicated by the absence of groundpotential on the test contact. During this time, relay 201 is preventedfrom operating in itssecond step by reason of the ground potential onboth terminals of its lower winding.

It may be assumed that the trunk line selected is the one comprisingconductors 224-226. Since wiper 222 encounters no ground potential, thecircuit which may be traced from ground on the release conductor 17 5,through the lower winding of relay 201, interrupting contacts 215,off-normal springs 218, through the winding of the stepping rela 203 tobattery, becomes eflective to cause re a 201 to operate in its secondstep. Due to t e high resistance of the lower winding of relay 201, thecurrent flow in the circuit is'insuflicient to cause the operation ofrelay 203. Relay 201, in operating to its second step, causes the fulloperation of all its armatures with the following results: At armature209 ground potential is supplied to the release conductor 225 of thelocal third selector S by way of ground on release conductor 175,working contact and armature 209, wiper 222, and the test contact 225 towhich conductor 225 is connected. The circuit for the upper winding ofrelay 201 is at the same time opened by the separation of contactscontrolled by armature 209. At armatures 208 and 211 the control circuitis extended to the selector S, ound now being supplied to the uppertalking conductor at springs controlled by armature 208,-and battery tothe lower talking conductor through vertical magnet 204 in series withrelay 202' at s rings controlled by armature 211.

The se ector S is identical in all details to the selector S andoperates responsive to the next series of impulses dialed by the callingsubscriber in a manner identical to the way in which selector Soperates, positioning. its wipers opposite the level of bank contactscorresponding to the digit dialled and then selecting an idle trunk inthis level.

It may be assumed that the trunk selected is the one comprisingconductor 234236 terminating at the connector 0. Thus,when this trunk isseized a circuit is closed for the upper winding of the two-step relay301 from ground supplied to release conductor 235, resting contact andarmature 313 through the upper winding of 301 to battery: Relay 301operates in its first stage operating armature 312 only, opening a pointin the circuit of release magnet 308. A circuit is also closed forswitching relay 305 from ground on conductor 235 through the normallyclosed vertical off-normal springs 333, through the lower winding ofrelay 305 to battery. Relay 305 operates and prepares a holding circuitfor itself at armature 328, and at armature 326 connects the verticalmagnet 306 in series with the series relay 302 at the same timedisconnecting the rotary magnet 307. Relay 305 at this time functions asa change-over relay as will be further described later. Seizure of thetrunk also causes the control circuit to be extended to the connector 0,ground now being supplied to the upper talking conductor at springscontrolled by armature 311, and battery to the lower talking conductorthrough vertical magnet 306 in series with relay 302 at springscontrolled by armature 315.

Responsive to the dialing of the next digit b the callin subscriber,resistance 136 and t e upper winding of relay 128 are again shortcircuited a corres onding number of times thereby causing the operationof the vertical magnet 306 to position the switch Wipers 341-343opposite the corresponding level of bank contacts. Series relay 302operates in series with the vertical magnet 306 and due to itsslow-acting characteristic remains operated during the transmission ofthe series of impulses. 'At armature 317 and the Working contact, theholding circuit for relay 305 is completed to maintain this relayoperated during the vertical movement of the switch wipers, the initialenergizing circuit for the lower winding of rela 305 eing opened on thefirst vertical step 0 the switch wipers at vertical off-normal spring333. The operation of armature 316 at this time is without effect. Atthe end of this series of impulses, relay 302 dcenergizes and opens theholding circuit of the lower winding of relay 305 at armature 317. Relay305 deenergizes and reconnects the rotary magnet 307 in series with therelay 302 at armature 326 at the same time disconnecting the verticalmagnet 306.

Responsive to the next series of impulses dialed by the callingsubscriber the rotary magnet 307 is operated to rotate the switch wipersinto engagement with the set of bank contacts corresponding to the digitdialed, this set being the one terminating the line of the calledsubstation A, namely bank contacts 344-346. Relay 302 again operatesduring the transmission of this series of impulses, this time in serieswith the rotary magnet 307, and prepares the testing circuit for thetest relay 304 at armature 316 and the working contact. The remainingoperations of the connector C now depend upon whether the called line isbusy or idle at this time.

If the line to substation A" is busy at this time, ground potential willbe present on the back contact 345, and the engagement of wiper 342 withcontact 345 completes a circuit for the test relay 304 from ground oncontact 345 by way of wiper 342, armature 316 and the working contact,resting contact and armature 327, through the winding of test relay 304to battery. Relay 304 operates and opens a point in the ring back tonecircuit at armature 323, closes a point in the busy tone circuit atarmature 322, and prepares a locking circuit for itself at armature 321.Shortly after the termination of this series of impulses, relay 302deenergizes, this time closing a locking circuit for test relay 304 bypermitting springs controlled by armature 316 to close. A circuit forthe lower winding of two-step relay 301 is also closed by the release ofarmature 317 which may be traced from ground on release conductor 235,rotary ofi-normal springs 331 closed upon the first rotary step of theswitch wipers, armature 317 and the resting contact, vertical olfnormalsprings 332 closed upon the first vertical step ofthe switch wipers,through the lower Wlnding of relay 301 to battery. The energization ofthe lower winding of this relay causes this relay tooperate in thesecond step, causing the full operation of all the armatur'es of thisrelay with the following results: At armature 313 the circuit for its'upper winding is opened, and at armatures 311 and 315 the ground andbattery supplied to conductors 234 and 236 are disconnected.

The disconnection of ground and battery.

from the conductors 234 and 236 causes the deenergization of the holdingrelay 128 in the first selector repeater SR. In deenergizing, relay 128opens the circuit of the supervisory relay 181 at armature 150, at thesame time placing ground potential on the release trunk directly. Bytherelease of armature 151, the lower winding of battery feedrelay 130 isconnected to the lower talking conduc tor. By the release of armatures148 and 152 a talking circuit is completed from the substation A to theconnector C,.so that the calling subscriber may hear the busy tone fromthe busy machine BM, a busy tone potential being supplied to the lowertalking conductor from the common busy tone conductor 391, restingcontact and armature 319, armature 322 and the Working contact, toconductor 236 from where it is transmitted to the calling substation.Hearing this tone notifies the calling subscriber that thedesired lineis busy at this time, whereupon he will replace his receiver with theintention of calling some later time. Replacing his receiver initiatesthe release of all the operated switches, this operation being fullydescribed in later paragraphs.

Returning now to the point where further operations of the connectorwere determined by the busy or idle condition of the calling line, itmay now be assumed that the line to.

substation A" is idle at the time connection relay 304 is not operated,no ground potential being present on thebank contact 345. In this case,when relay 302 falls back at the termination of the impulses, a circuitis closed which may be traced from ground on release conductor 235,armature 321 and the resting contact, through the upper winding of relay305, resting contact and armature 316, wiper 342, bank contact 345through the winding of the switching relay 361 of the lineswitch LS",interrupting contacts 369, through the winding of the magnet 363 tobattery. Relays 305 and 361 operate in this circuit, but due to the highresistance of the switching relay 361, the current flow is insuflicientto cause the operation of magnet 363. Relay 305, in operating, closes alocking circuit for itself at armature 328, places ground potential onthe bank contact 345 at armature 325 by way of wiper 342, therebymarking the line of substation A" busy, and

at armatures 324 and 329 closes the signalling circuit to signal thesubscriber at substation A". The signaling circuit may be traced fromground by way of the resting contact and armature 318, armature 324 andthe working contact, wiper 341, bank contact 344, line conductor 371through the balls of the substation A", line conductor 372, bank contact346, wiper 343, working contact and armature 329, armature 320 and theresting contact, through the lower winding of ring cut-otf relay 303,common signalling conductor 390 to which battery superimposed ring ingccurrent from generator G and direct battery are intermittentlyconnected. Relay 361 in energizing, disconnects the normal ground andbattery connections from the line conductors without connecting up theswitch wipers 380-382, this being due to the usual mechanicalinterlocking mechanism between relays 361 and 362. The bells at thesubstation A" now operate responsive to the ringing current until thesubscriber at substation A" answers. Obviously, relay 301 is againoperated in its second step at the end of the last series of impulses,the circuit for its lower winding being closed by the release ofarmature 317, after which relay 128 in the selector repeater SR isdeenergized, preparing the talking circuit by releasing armatures 148and 152 as reviously described.

When the su scriber at substation A" removes his receiver to answer thecall, a direct current bridge is placed across the line conductors371372 which closes a direct current circuit for the ring cut-off relay303. Ring cut-off relay 303 operates and closes a locking circuit forits upper winding at armature 319' which may be traced from ground onrelease conductor 235, armature 319 and the working contact, through theupper winding of relay 303,. resistance 309 to battery. At armatures 318and 320 the ringing circuit is disconnected and the talking circuitbetween the subscribers at sub station A and substation A is finallycomacross the called ine.

pleted. The release of armatures 148 and 152 bridges batter feed relay130 directly Relay 130 operates and disconnects one terminal of relay128 from the lower talking conductor at armature 158; reverses theground and battery connections to the calling line at armatures 155 and156; and at armature'157'closes a circuit for the magnet 116 of thesubscribers meter M in parallel with the lower winding of relay 129. Themeter M operates to register the callf Relay 129 operates andlocks tothe release trunk at armature 153, and functions to maintainthe circuitof magnet 116 closed u'ntil'the connection is released. In :"this waythe meter M is prevented from being falsely operated by the jiggling ofthe receiver switchhook at the called station.

The reversing of the battery and ground conthe line, talking batternections to the calling line performs no function in the presentconnection. This operation may be used to cause the collection of a coinwhen a call is initiated from a pay station, and is therefore shown herefor the purpose of illustration. The calling and called subscribers maynow hold conversation, relays 125 and 130 being the only brid es acrossbeing urnished through the windings of relay 125 for the callingsubscriber and through the windings of rela 130 for the calledsubscriber.

At the end of the conversation both subscribers will replace theirreceivers. lVhen the called subscriber replaces his receiver, the directcurrent bridge across the line conductors is opened thereby causing thedeenergization of the battery feed relay 130. Relay 130 deenergizes andrestores its armatures to normal. The direction of current flow to thecalling substation is restored to normal by the release of armatures 155and 156, and-a circuit for the supervisory lamp L and relay 182 isclosed at armature 157. When the calling subscriber replaces hisreceiver, the direct current bridge across the line conductors 101 and103 is mterrupted thereby opening the circuit for the line relay 126.Relay 126 deenergizes and opens the circuit of release relay 127 atarmature 142. Relay 127 deenergizes and releases its armatures with thefollowing results: At armature 144 ground potential is removed from therelease conductor 122, and a circuit, which-includes the off-normalsprings 168 closed upon the first vertical step of the switch wipers andarmature 138, is closed for the release magnet 135. "In operating,magnet 135 restores the switch wipers 171-173 to normal. The removal ofground from release conductor 122 also opens the holding circuit for thelower winding of relay 129, and removes ground otential from the meterconductor123. Reays 129 and 105 thereupon deenergize and restore theirarmatures to normal; magnet 116 of the subscribers meter M restores tonormal.

By the release of armature 145, ground potential is removed from therelease conductors 122, 225, and 235, which are serially connected,extending through the first selector repeater SR, second selector Sthird selector S and connector C. The removal of ground from theserespective conductors causes the deenergization of switching relay 132in the selector repeater SR, switching rela 201 in the second selector Sswitching re ay 201 in the third selector S and switching relay 301 inthe connector 0. The deenergization of the above mentioned switchingrelays efi'ect the closure of the following release circuits: A circuitfor release magnet 206 is closed from ground by way of armature 210 andthe resting contact, Vertical 011- normal springs 217 closed upon thefirst vertical step of the wipers 221-223 of selector S, through thewinding of release magnet 206 to battery. Release ma net 206 operatesand causes the restoration of the wipers 221 223 of the selector 8.Similarly, a circuit is closed for release magnet 206 of the thirdselector S which magnet operates to release wipers 231233 of theselector S to normal. A circuit is also closed for release magnet 308which may be traced from ground by way of the resting contact andarmature 312, vertical ofi-normal springs 330 closed upon the firstvertical step of the connector C, through the winding of the releasemagnet 308 to battery. Magnet 308 operates and causes the restoration ofthe wipers 341-343 of the connector C to normal. The removal of groundpotential from the release conductor 235 also opens the holding circuitsfor the ring outofi relay 303, and switching relay 305. These relaysthereupon deenergize and restore their armatures to normaL- Allapparatus used in establishing the above described connection has nowbeenrestored'to normal and is ready to be used again to establish otherconnections.

Uall from distant o fice t0 substation A use of outgoing repeaters isentirely obviated,

the trunks extending from one exchange to another being accessibledirectly in the banks of first selector repeaters of the type shown inFig. 1 (or Fig. 9, to be described later) and terminating directly inincoming selector repeaters such as shown in Fig. 4. To describe theoperations performed in establishing a connection from a subscriber inone office to a subscriber in another office, it will be assumed that acertain subscriber 1n some distant oflice desires connection with thesub-u scriber at substation A, (drawings to be arranged as shown in Fig.11)

Toestablish this connection, the subscriber in the distant ofliceremoves his receiver and dials the directory number of the substation A.In response-to the removal of the receiver at the calling substation theindividual lineswitch of the said substation operates to select a trunkto an idle first selector repeater, which ma be identical to the firstselector repeater s own in Fig. 1.' Responsive to the dialing of thefirst digit of the called number, the first selector repeater operatesas described above and positions its wipers opposite the level of thebank contact in which trunks to the oflice serving the subscriber atsubstation A are accessible, and

then automaticall select an idle one of'these trunks. It may eassumedthat the'trunk selected is the one comprising conductors 401 and 402terminatin in the incoming second selector IS, Fig. 4. hen this trunk isseized,

. a circuit is closed which may be traced from ground by way of theresting contact and armature 419 in the incomin selector IS, through thewinding of line re ay 403, trunk conductor 401, over a loop including aresistance and the holding relay of the selected firstselector repeatersimilar to resistance 136 and relay 128 of selector repeater $18., overtrunk conductor 402, armature 420 and the resting contact, through theupper winding of the marginal-1y adjusted impulse relay 405 of theincoming selector IS to battery. The resistance of the above tracedcircuit is sufiiciently high to prevent the operation of relay 405 atthis time. Relay 403 is partially shunted by the-ground connection byway of resting contact and armature 418 and resistance 440 butnevertheless operates over the above traced circuit and performs thefollowing circuit changes: At armature 415 an obvious circuit is closedfor release relay 408. Relay 408 operates and at armature 428 opens apoint in the circuit of release magnet 413 and connects ground potentialto release conductor 450. Relay 403 in operating also closes a circuitwhich may be traced from ground by way of the normally closed springscontrolled by armature 431, armature 416 and the working contact,armature 417 and the resting contact, resistance 441, through the windinof the holding relay 406, normally close vertical off-normal springs436, normally closed springs controlled by armature' 435, restingcontact and armature 449, through the winding of series relay 409,through the winding of vertical magnet 412 to battery. The current flowin this circuit is insufficient to cause the operation of magnet 412 andseries relay 409 at this time, but holding rela 406 energizes and atarmature 424 shunts t e ofi-normalsprings 436 which are opened upon thefirst vertical step of the switch wipers, prepares the holding circuitfor stepping relay 407 at armature 423, and at armature 425 prepares adeenergizing circuit for impulse relay 405. p

Responsive to the next series of impulses dialed by the callingsubscriber, the resistance and relay in the selected first selectorrepeater at this oiiice similar to resistance 136 and relay 128 ofselector SR, Fig. l, are short circuited by contacts on theline relay anumber of times corresponding to the 2 digit dialled, as previouslydescribed. Each time that this resistance and relay are short circuited,the current flow in the above traced circuit includingthe two trunkconductors in series is sufficiently increased to cause the operation ofthe marginal relay 405. Marginal relay 405, in operating, closes acircuit for the lower winding of relay 405 at armature 422 which may etraced from ground by way of armature 422 and the working contact,armature 425 and the working contact, resistance 442, normally closedsprings controlled by armature 419, through the lower winding of relajy405 to battery. Marginal relay 405 is di erentially wound with thewindings so proportioned that the magneto motive force produced by thecurrent in the upper winding when the resistance and winding of theimpulsing relay in the first selected repeater are short circuited, isgreater than that produced by the lower winding. For this reason relay405 remains operated dur ing the time the resistance and the impulsingrelay of the first selected repeater are short circuited. But when theshort circuit is removed from the said relay and resistance, the currentflow in the upper winding of relay 405 is reduced so that the magnetomotive force produced by the current in the lower winding is greaterthan that produced by v the current in the upper winding. Relay 405therefore immediately deenergizes and in so doing opens the circuit ofits own lower winding at'armature 422. In this manner, the impulse relay405 operates in positive syn chronism with the line relay of the firstse-- lector repeater. Each time relay 405 operates, resistance 441 andrelay 406 are short circuited. This causes impulses of increased currentin the circuit of magnet 412 and series relay 409. As a result magnet412 is operated to raise the wipers 451-453 of the incoming selector ISopposite the level of bank contacts corresponding to the digit dialed.Series relay 409 operates in series with the magnet 412, remainingoperated continuously during the transmission of the series of impulsesby reason of its slow acting characteristic, and closing a circuit forthe stepping relay 407. This circuit may be traced from ground by way ofarmature 428 and the working contact, working contact and armature 429,armature 434 and the resting contact, ofi-normal springs 437 closed uponthe first vertical step of the switch wipers, through the winding ofstepping relay 407 to battery. Stepping relay 407 operates and closes aholding circuit for itself at armature 426 which may be traced fromground by way of armature 423 and the working contact, armature 426 andthe working contact, interrupting springs 439, off-normal springs 437,through the winding of relay 407 to battery. .At armature 427 a circuitis prepared for the rotar magnet 414.

t the termination of this series of impulses, series relay 409de-actuates and closes a circuit for magnet 414 which may be traced fromground by way of armature 428 and the working contact, normally closedsprings con trolled by armature 429, working contact and armature 427through the winding of rotary set of contacts is busy, ground potentialwill be present on the test contact engaged by wiper 452, and relay 407will again be energized. Thus stepping relay 407 and magnet 414 operatealternately and cause the switch wipers to be moved into engagement witha set of bank contacts terminating an idle trunk, in the well knownmanner.

When the contacts terminating atthe idle trunk are reached, which may beassumed to be the trunk comprising conductors 454456, no groundpotential will be encountered by wiper 452, and the circuit which may betraced from ground by way of armature 428 and the working contact,through the winding of relay 411, interrupting contacts 439,ofi'-norn1al springs 437, through the windin Y of stepping relay 407 tobattery, becomes e fective to energize switching relay 411. Due to theresistance of switching relay 411, the current flow in this circuit isinsuflicient to cause the operation of stepping relay 407. Switchingrelay 411 operates, however, and performs circuit changes as follows: Atarmature 433 ground potential is supplied to release conductor 455 byway of armature 428 and the working contact; a circuit is prepared forswitchover relay 404 at armature 432; the initial energizing circuit ofrelay 407 is opened at armature 434; and at armature 431 and 435 groundand battery via magnet 412 is disconnected from the heavy talkingconductors by the separation of the normally closed springs controlledby these armatures step, thereby preparing the selector for operat1on.,

Responsive to the next series of impulses dialed by the callingsubscriber, relay 405 is again operated a corresponding number of times,short circuiting relay 406 and resistance'441 the same number of times,which causes the operation of the verticalmagnet

